1. Field of the Invention:
This invention relates to a curable composition capable of producing cured articles excelling in thermal stability, especially hydrothermal stability, a method for the production of the composition, and uses thereof. More particulary the present invention relates to a curable composition obtained by dispersing an inorganic filler of a specific particle diameter in a specified liquid monomer mixture, a method for the production of the composition, and uses of the composition for artificial marble articles.
2. Description of Prior Art:
Curable resin composition prepared by dispersing various fillers in syrups of such thermosetting resins as unsaturated polyester resin, vinyl ester resin obtained by dissolving epoxy (meth)acrylate in styrene, and epoxy resin have been known to the art. They have been being used for cast molding artificial marble articles and for molding FRP in combination with glass fibers. It has been known to mold artificial marble articles by causing a resin composition prepared by dispersing a filler in a thermoplastic resin syrup such as, for example, a blend of aluminum hydroxide with a syrup of methyl methacrylate, to be set with an organic peroxide as a curing agent (U.S. Pat. No. 3,847,865). These thermosetting resin or thermoplastic resin syrups are molded conventionally by being poured into molds of various shapes or a space between moving belts and then heated to temperatures ranging from normal room temperature to the neighborhood of 60.degree. C. Curable resin compositions of the type to be compression or extrusion molded under application of heat and pressure in metal molds have been also known to the art. Resin mortar or premix molding materials prepared by mixing such thermosetting resins as unsaturated polyester resin and vinyl ester resin with various fillers and aggregates and, optionally, incorporating in the resulting mixtures glass fibers and thickners for the purpose of enhancing viscosity are examples.
The curable resin compositions using the syrups and used for the cast molding are such that the amounts and sizes of the fillers effectively usable therein have their own limits because the compositions are required to maintain their viscosity low enough to suit cast molding. When a filler is used in a large amount for the purpose of obtaining a cured article of a high filler content excelling in thermal stability and flame retardance, the produced cured article does not assume good appearance because the filler is not easily diffused in the syrups during the preparation of the composition. For the purpose of preventing the high filler content from increasing the viscosity of the produced curable resin composition, there is employed, for example, a method which resorts to selection of a filler of the largest possible particle diameter that entails no sedimentation. The cured article obtained by polymerizing such a curable resin composition as described above, therefore, has the disadvantage that it sustains a cracking the surface because of insufficient filler dispersion or because of large particle diameters of filler and consequently admits of water and, on being immersed in boiling water, quickly blushes and loses its good appearance.
In the case of the aforementioned curable resin composition using resin mortar or premix molding materials and used for molding under simultaneous application of heat and pressure, the amounts of their fillers allowed to be incorporated in producing doughlike masses excelling in workability during the compression molding have their own limits. Generally, the upper limits of these amounts are 200 parts by weight based on 100 parts by weight of the resin. In the cured products obtained by polymerizing such curable resin compositions, the resins show poor adhesion to the fillers or aggregates and the resins offer poor resistance to water. The cured products have a disadvantage that, when they are immersed in boiling water, they quickly sustain damage to the surface and blush and lose luster. Further, these cured products are deficient in thermal stability and are susceptible of discoloration at elevated temperatures. In a burning cigerret test, they are conspicuously stained with tar. In applications such as bathtubs, dressing tables, button blank, electric parts, and kitchen counters which require resistance to flame, heat and hot water, the conventional curable resin compositions manifest insufficient performance.
A method of imparting improved hydrothermal stability to the cured products of such curable resin compositions by gel coating the cured products with unsaturated polyester resin or vinyl ester resin has found acceptance. The cured products which have undergone the gel coating treatment, however, have the disadvantage that they are deficient in thermal stability so as to sustain irreparable blisters and other similar blemishes on exposure to a burning cigerret or hot water.
An object of this invention, therefore, is to provide a novel curable composition, a method for the production of the curable composition, and uses of the curable composition.
Another object of this invention is to provide a curable composition capable of affording cured products excelling in thermal stability and flame retardance without requiring any gel coating treatment, a method for the production of the curable composition, and uses of the curable composition.